Erythromycins A through D, represented by formula (I), ##STR2## are well-known and potent antibacterial agents, used widely to treat and prevent bacterial infection. As with other antibacterials, however, bacterial strains having resistance or insufficient susceptibility to erythromycin have been identified. Also, erythromycin A has only weak activity against Gram-negative bacteria. Therefore, there is a continuing need to identify new erythromycin derivative compounds which possess improved antibacterial activity, which have less potential for developing resistance, which possess the desired Gram-negative activity, or which possess unexpected selectivity against target microorganisms. Consequently, numerous investigators have prepared chemical derivatives of erythromycin in an attempt to obtain analogs having modified or improved profiles of antibiotic activity.
Morimoto et al. described the preparation of 6-O-methyl erythromycin A in J. Antibiotics 37:187 (1984). Morimoto et al. further disclosed a series of O-alkyl erythromycin A derivatives in J. Antibiotics 43: 286 (1990). In their experience, "O-alkylation, other than methylation, took place at the C-11 hydroxyl group exclusively." However, in European Patent Application 272,110, published Jun. 22, 1988, Morimoto et al. disclose 6-O-C.sub.1 -C.sub.3 -alkyl erythromycin A compounds.
In European Patent Application 215,355, published Mar. 28, 1987, Omura and Itoh disclose 6-O-loweralkyl erythromycins as stimulants of gastrointestinal contractile motion.